What’s the Internet: “nuts and bolts” view
‰ millions of connected
computing devices: hosts
Lecture 5: Data Communications
and Internet Technology
= end systems
‰ running network apps
‰ communication links
Dr Hui Xiong
Dr.
Rutgers University


‰
router
workstation
server
mobile
local ISP
fiber, copper, radio,
fib
di
satellite
transmission rate =
regional ISP
bandwidth
routers: forward packets
(chunks of data)
company
network
Introduction
What’s the Internet: “nuts and bolts” view
‰
protocols control sending,
receiving of msgs

‰
router
e.g., TCP, IP, HTTP, FTP, PPP
‰ communication
infrastructure enables
distributed applications:
mobile
local ISP
Internet: “network of

networks”


Web, email, games, ecommerce, file sharing
‰ communication
mm
services
lloosely
l hierarchical
h
h l
public Internet versus
private intranet
provided to apps:
regional ISP


‰ Internet standards
 RFC: Request for comments
 IETF: Internet Engineering
Task Force
Connectionless unreliable
connection-oriented
reliable
company
network
Introduction
Introduction
1-3
What’s a protocol?
What’s a protocol?
human protocols:
‰ “what’s the time?”
‰ “I have a question”
‰ introductions
a human protocol and a computer network protocol:
… specific msgs sent
… specific actions taken
when msgs received,
or other events
1-2
What’s the Internet: a service view
workstation
server
Introduction
1-1
network protocols:
1-4
‰ machines rather than
humans
Hi
‰ all communication
activity in Internet
governed by protocols
Hi
TCP connection
response
Got the
time?
protocols define format,
order of msgs sent and
received among network
entities, and actions
taken on msg
transmission, receipt
Introduction
TCP connection
req
Get http://www.awl.com/kurose-ross
2:00
<file>
time
Q: Other human protocols?
1-5
Introduction
1-6
1
The network edge:
A closer look at network structure:
‰ end systems (hosts):
‰ network edge:

applications and
hosts
‰ network core:




run application programs
e.g. Web, email
at “edge of network”
‰ client/server model
routers
network of
networks


‰ access networks,
client host requests, receives
service from always-on server
e.g. Web browser/server;
email client/server
‰ peer-peer model:
physical media:
communication links


Introduction
minimal (or no) use of
dedicated servers
e.g. Gnutella, KaZaA
Introduction
1-7
The Network Core
Network Core: Circuit Switching
‰ mesh of interconnected
End-end resources
reserved for “call”
routers
‰ the fundamental
question: how is data
transferred through net?
 circuit switching:
dedicated circuit per
call: telephone net
 packet-switching: data
sent thru net in
discrete “chunks”
‰ link bandwidth, switch
capacity
‰ dedicated resources:
no sharing
‰ circuit-like
(guaranteed)
performance
‰ call setup required
Introduction
‰ pieces allocated to calls
‰ resource piece
idle if
Introduction
1-9
1-10
Circuit Switching: FDM and TDM
Network Core: Circuit Switching
network resources
(e.g., bandwidth)
divided into “pieces”
1-8
Example:
‰ dividing link bandwidth
FDM
into “pieces”
 frequency division
 time division
4 users
frequency
not used by owning call
time
(no sharing)
TDM
frequency
Introduction
1-11
time
Introduction
1-12
2
Network Core: Packet Switching
each end-end data stream
divided into packets
‰ user A, B packets share
network resources
‰ each packet uses full link
bandwidth
‰ resources used as needed
Bandwidth division into “pieces”
Dedicated allocation
Resource reservation
Packet Switching: Statistical Multiplexing
resource contention:
demand can exceed
amount available
‰ congestion: packets
queue, wait for link use
‰ store and forward:
packets move one hop
at a time

Node receives complete
packet before forwarding
Introduction
10 Mb/s
Ethernet
A
‰ aggregate resource
C
statistical multiplexing
1.5 Mb/s
B
queue of packets
waiting for output
link
D
E
Sequence of A & B packets does not have fixed
pattern Î statistical multiplexing.
In TDM each host gets same slot in revolving TDM
frame.
Introduction
1-13
Packet switching versus circuit switching
Packet switching versus circuit switching
Packet switching allows more users to use network!
Is packet switching a “slam dunk winner?”
‰ 1 Mb/s link
‰ Great for bursty data
‰ each user:
 100 kb/s when “active”
 active 10% of time
resource sharing
simpler, no call setup
‰ Excessive
E
i congestion:
i
packet
k d
delay
l and
d lloss
 protocols needed for reliable data transfer,
congestion control
‰ Q: How to provide circuit-like behavior?
 bandwidth guarantees needed for audio/video
apps
 still an unsolved problem (chapter 6)
‰ circuit-switching:
 10 users


N users
1 Mbps link
‰ packet switching:
 with 35 users,
probability > 10 active
less than .0004
Introduction
Introduction
1-15
Telecommunication
networks
L
‰ Takes L/R seconds to
R
transmit (push out)
packet of L bits on to
p
link or R bps
‰ Entire packet must
arrive at router before
it can be transmitted
on next link: store and
1-16
Network Taxonomy
Packet-switching: store-and-forward
R
1-14
R
Example:
‰ L = 7.5 Mbits
‰ R = 1.5
1 5 Mbps
‰ delay = 15 sec
Circuit-switched
networks
FDM
TDM
Packet-switched
networks
Networks
with VCs
Datagram
Networks
• Datagram network is not either connection-oriented
or connectionless.
• Internet provides both connection-oriented (TCP) and
connectionless services (UDP) to apps.
forward
‰ delay = 3L/R
Introduction
1-17
Introduction
1-18
3
Access networks and physical media
Residential access: point to point access
Q: How to connect end
systems to edge router?
‰ Dialup via modem
up to 56Kbps direct access to
router (often less)
 Can’t surf and phone at same
time: can
can’tt be “always
always on
on”
‰ residential access nets

‰ institutional access
networks (school,
company)
‰ mobile access networks
‰ ADSL: asymmetric digital subscriber line
up to 1 Mbps upstream (today typically < 256 kbps)
up to 8 Mbps downstream (today typically < 1 Mbps)
 FDM: 50 kHz - 1 MHz for downstream
Keep in mind:

‰ bandwidth (bits per

second) of access
network?
‰ shared or dedicated?
4 kHz - 50 kHz for upstream
0 kHz - 4 kHz for ordinary telephone
Introduction
1-19
Residential access: cable modems
Introduction
1-20
Introduction
1-22
Introduction
1-24
Residential access: cable modems
‰ HFC: hybrid fiber coax
asymmetric: up to 30Mbps downstream, 2
Mbps upstream
‰ network of cable and fiber attaches homes to
ISP router
 homes share access to router
‰ deployment: available via cable TV companies

Introduction
1-21
Cable Network Architecture: Overview
Diagram: http://www.cabledatacomnews.com/cmic/diagram.html
Cable Network Architecture: Overview
Typically
yp
y 500 to 5,000
,
homes
cable headend
cable distribution
network (simplified)
cable headend
home
cable distribution
network (simplified)
Introduction
1-23
home
4
Cable Network Architecture: Overview
Cable Network Architecture: Overview
FDM:
server(s)
V
I
D
E
O
V
I
D
E
O
V
I
D
E
O
V
I
D
E
O
V
I
D
E
O
V
I
D
E
O
D
A
T
A
C
O
N
D T
A R
T O
A L
1
2
3
4
5
6
7
8
9
Channels
cable headend
cable headend
home
cable distribution
network
cable distribution
network
Introduction
1-26
Wireless access networks
wireless access
network connects end system
to router
‰ shared
‰ company/univ local area
network (LAN) connects
end system to edge router
‰ Ethernet:
 shared or dedicated link
connects end system
and router
 10 Mbs, 100Mbps,
Gigabit Ethernet
‰ LANs: chapter 5

via base station aka “access
point”
‰ wireless LANs:
 802.11b (WiFi): 11 Mbps
router
base
station
‰ wider-area wireless access
 provided by telco operator
 3G ~ 384 kbps
• Will it happen??
 WAP/GPRS in Europe
Introduction
mobile
hosts
Introduction
1-27
Home networks
1-28
Physical Media
Typical home network components:
‰ ADSL or cable modem
‰ router/firewall/NAT
‰ Ethernet
‰ wireless access
point
cable
modem
Introduction
1-25
Company access: local area networks
to/from
cable
headend
home
router/
firewall
Ethernet
‰ Bit: propagates between
transmitter/rcvr pairs
‰ physical link: what lies
wireless
laptops

signals propagate in solid
media: copper, fiber, coax


Category 3: traditional
phone wires, 10 Mbps
Ethernet
Category 5:
100Mbps Ethernet
‰ unguided media:
 signals propagate freely,
e.g., radio
wireless
access
point
Introduction
between transmitter &
receiver
‰ guided media:
Twisted Pair (TP)
‰ two insulated copper
wires
1-29
Introduction
1-30
5
Figure 5-7 NIC Interface Card
Physical Media: coax, fiber
Coaxial cable:
‰ two concentric copper
conductors
‰ bidirectional
‰ baseband:


single channel on cable
legacy Ethernet
‰ broadband:
 multiple channel on cable
 HFC
Fiber optic cable:
‰ glass fiber carrying light
pulses, each pulse a bit
‰ high-speed operation:
 high-speed point-to-point
transmission (e
(e.g.,
g 5 Gps)
‰ low error rate: repeaters
spaced far apart ; immune
to electromagnetic noise
Introduction
Figure 5-8 Unshielded Twisted Pair (UTP) Cable
Introduction
electromagnetic
spectrum
‰ no physical “wire”
‰ bidirectional
‰ propagation
environment effects:



reflection
obstruction by objects
interference
1-32
Figure 5-9 Optical Fiber Cable
Introduction
1-33
Physical media: radio
‰ signal carried in
Introduction
1-31
1-34
Internet structure: network of networks
Radio link types:
‰ terrestrial microwave
 e.g. up to 45 Mbps channels
‰ LAN (e.g., Wifi)
 2Mbps, 11Mbps
‰ wide-area (e.g., cellular)
 e.g. 3G: hundreds of kbps
‰ satellite
 up to 50Mbps channel (or
multiple smaller channels)
 270 msec end-end delay
 geosynchronous versus low
altitude
Introduction
1-35
‰ roughly hierarchical
‰ at center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity,
Sprint, AT&T), national/international coverage
 treat each other as equals
Tier-1
providers
interconnect
(peer)
privately
Tier 1 ISP
Tier 1 ISP
NAP
Tier-11 p
Ti
providers
id s
also interconnect
at public network
access points
(NAPs)
Tier 1 ISP
Introduction
1-36
6
Tier-1 ISP: e.g., Sprint
Internet structure: network of networks
Sprint US backbone network
‰ “Tier-2” ISPs: smaller (often regional) ISPs
 Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs
Tier-2 ISP
Tier-2 ISP pays
tier-1 ISP for
connectivity to
rest of Internet
‰ tier-2 ISP is
customer of
tier-1 provider
Tier 1 ISP
Locall and
L
d tieri
3 ISPs are
customers of
higher tier
ISPs
connecting
them to rest
of Internet
Tier-2 ISP
local
ISP
local
ISP
Tier 3
ISP
Tier-2 ISP
local
ISP
local
ISP
Tier-2 ISP
local
ISP
Introduction
Tier-2 ISP
local
local
ISP
ISP
1-39
‰ 1. nodal processing:
 check bit errors
 determine output link
‰ packet arrival rate to link exceeds output link capacity
‰ packets queue, wait for turn
packet
k t being
b i ttransmitted
itt d (delay)
(d l )
A
Tier-2 ISP
local
ISP
Introduction
1-40
propagation
B
packets queueing (delay)
1-41
‰ 2. queueing
 time waiting at output
link for transmission
 depends on congestion
level of router
transmission
A
Introduction
Tier-2 ISP
local
ISP
Four sources of packet delay
packets queue in router buffers
free (available) buffers: arriving packets
dropped (loss) if no free buffers
NAP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISP
How do loss and delay occur?
B
local
ISP
Tier 1 ISP
NAP
Tier-2 ISP
local
ISP
1-38
‰ a packet passes through many networks!
local
ISP
Tier-2 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISP
local
local
ISP
ISP
Introduction
local
ISP
Tier 1 ISP
Tier-2 ISP
Internet structure: network of networks
‰ “Tier-3” ISPs and local ISPs
 last hop (“access”) network (closest to end systems)
Tier 3
ISP
Tier-2 ISPs
also
l peer
privately with
each other,
interconnect
at NAP
Tier-2 ISP
1-37
Internet structure: network of networks
local
ISP
NAP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISP
Introduction
Tier-2 ISP
nodal
processing
queueing
Introduction
1-42
7
An Example: Caravan analogy
Delay in packet-switched networks
3. Transmission delay:
‰ R=link bandwidth (bps)
‰ L=packet length (bits)
‰ time to send bits into
link = L/R
‰ s = propagation speed in
medium (~2x108 m/sec)
nodal
processing
queueing
Introduction
100 km
toll
booth
toll
booth
100 km/hr
‰ Toll booth takes 12 sec to
service a car
(transmission time)
‰ car~bit; caravan ~ packet
‰ Q: How long until caravan
is lined up before 2nd toll
booth?
propagation
B
ten-car
caravan
‰ Cars “propagate” at
‰ p
propagation
p g
delay
y = d/s
Note: s and R are very
different quantities!
transmission
A
100 km
4. Propagation delay:
‰ d = length of physical link
‰ Time to “push” entire
caravan through toll
booth onto highway =
12*10 = 120 sec
‰ Time for last car to
propagate from 1st to
2nd toll both:
100km/(100km/hr)= 1 hr
‰ A: 62 minutes
Introduction
1-43
Packet loss
1-44
Protocol “Layers”
Networks are complex!
‰ many “pieces”:
 hosts
 routers
 links of various
media
 applications
 protocols
 hardware,
software
‰ queue (aka buffer) preceding link in buffer
has finite capacity
‰ when packet arrives to full queue, packet is
pp (aka lost)
dropped
‰ lost packet may be retransmitted by
previous node, by source end system, or
not retransmitted at all
Introduction
Question:
Is there any hope of
organizing structure of
network?
Or at least our discussion
of networks?
Introduction
1-45
1-46
Layering of airline functionality
Organization of air travel
ticket (purchase)
ticket (complain)
ticket (purchase)
ticket (complain)
ticket
baggage (check)
baggage (claim)
baggage (check)
baggage (claim
baggage
gates (unload)
gate
gates (unload)
gates (load)
gates (load)
runway (takeoff)
runway (land)
takeoff/landing
runway takeoff
runway landing
airplane routing
airplane routing
airplane routing
departure
airport
airplane routing
airplane routing
airplane routing
airplane routing
intermediate air-traffic
control centers
arrival
airport
Layers: each layer implements a service
 via its own internal-layer actions
 relying on services provided by layer below
airplane routing
‰ a series of steps
Introduction
1-47
Introduction
1-48
8
Why layering?
Internet protocol stack
Dealing with complex systems:
‰ application: supporting network
applications
‰ explicit structure allows identification,
relationship of complex system’s pieces
 layered reference model for discussion
‰ modularization eases maintenance, updating of
system
 change of implementation of layer’s service
transparent to rest of system
 e.g., change in gate procedure doesn’t affect
rest of system
‰ layering considered harmful?

source
datagram Hn Ht
frame
Hl Hn Ht
M
M
M
M
transport
‰ network: routing of datagrams from
network

M
link
physical

‰ physical: bits “on the wire”
Introduction
Hl Hn Ht
M
M
Hn Ht
M
Hl Hn Ht
M
application
transport
network
link
physical
M
Hl Hn Ht
M
network
link
physical
Hn Ht
M
Hl Hn Ht
M
1-50
IP Addressing: introduction
M


router
Introduction
223.1.1.1
identifier for host,
router interface
‰ interface: connection
between host/router
and physical link

Ht
PPP, Ethernet
1-49
switch
Hn Ht
physical
neighboring network elements
‰ IP address: 32-bit
Hl Hn Ht
destination
link
IP, routing protocols
‰ link: data transfer between
Encapsulation
application
transport
network
link
physical
‰ transport: host-host data transfer
 TCP, UDP
source to destination
Introduction
message
segment Ht
application
FTP, SMTP, STTP
router’s typically have
multiple interfaces
host may have multiple
interfaces
IP addresses
associated with each
interface
223.1.2.1
223.1.1.2
223.1.1.4
223.1.1.3
223.1.3.27
223.1.2.2
223.1.3.2
223.1.3.1
223.1.1.1 = 11011111 00000001 00000001 00000001
223
1
1
Introduction
1-51
IPv6
223.1.2.9
1
1-52
MAC Addresses and ARP
‰ Initial motivation: 32-bit address space soon
‰ 32-bit IP address:
to be completely allocated.
‰ Additional motivation:
header format helps speed processing/forwarding
 header changes to facilitate QoS


network-layer address

used to get datagram to destination IP subnet
‰ MAC (or LAN or physical or Ethernet)
address:

Introduction
1-53
48 bit MAC address (for most LANs)
burned in the adapter ROM
Introduction
1-54
9
LAN Address (more)
Elements of a wireless network
‰ MAC address allocation administered by IEEE
‰ manufacturer buys portion of MAC address space
(to assure uniqueness)
‰ Analogy:
network
infrastructure
((a)) MAC address:
dd
like
lik Social
S i lS
Security
it N
Number
b
(b) IP address: like postal address
‰ MAC flat address ➜ portability

wireless hosts
‰ laptop, PDA, IP phone
‰ run applications
‰ may be stationary
(non-mobile) or mobile

wireless does not
always mean mobility
can move LAN card from one LAN to another
‰ IP hierarchical address NOT portable
 depends on IP subnet to which node is attached
Introduction
Introduction
1-55
Elements of a wireless network
Elements of a wireless network
base station
wireless link
‰ typically connected to
network
infrastructure
1-56
wired network
‰ relay - responsible
for sending packets
between wired
network and wireless
host(s) in its “area”
 e.g., cell towers
802.11 access
points
Introduction
‰ typically used to
network
infrastructure
Introduction
1-57
Multimedia, Quality of Service:
What is it?
1-58
MM Networking Applications
Multimedia applications:
network audio and video
(“continuous media”)
Classes of MM applications:
1) Streaming stored audio
and video
2) Streaming live audio and
video
3) Real-time interactive
audio and video
QoS
network provides
application with level of
Jitter is the variability
of packet delays within
the same packet stream
performance needed for
application to function.
Introduction
connect mobile(s) to
base station
‰ also used as backbone
link
‰ multiple access
protocol coordinates
link access
‰ various data rates,
transmission distance
1-59
Fundamental
characteristics:
‰ Typically delay sensitive
 end-to-end delay
 delay jitter
‰ But loss tolerant:
infrequent losses cause
minor glitches
‰ Antithesis of data,
which are loss intolerant
but delay tolerant.
Introduction
1-60
10
Streaming Multimedia: Client
Buffering
Streaming Stored Multimedia
Streaming:
‰ media stored at source
‰ transmitted to client
‰ streaming: client playout begins
before all data has arrived
constant
drain
rate, d
variable fill
rate, x(t)
buffered
video
‰ timing constraint for still-to-be
transmitted data: in time for playout
‰ Client-side buffering, playout delay
Introduction
1-61
Streaming Multimedia: client
rate(s)
compensate for network-added delay, delay
jitter
Introduction
1-62
What is network security?
1.5 Mbps encoding
Confidentiality: only sender, intended receiver
should “understand” message contents
 sender encrypts message
 receiver decrypts message
A th ti ti
Authentication:
sender,
d
receiver
i
wantt tto confirm
fi
identity of each other
Message Integrity: sender, receiver want to ensure
message not altered (in transit, or afterwards)
without detection
Access and Availability: services must be accessible
and available to users
28.8 Kbps encoding
Q: how to handle different client receive
rate capabilities?
 28.8 Kbps dialup
 100Mbps Ethernet
A: server stores, transmits multiple
copies of video, encoded at
Introduction
different rates
Introduction
1-63
Friends and enemies: Alice, Bob, Trudy
1-64
There are bad guys (and girls) out there!
‰ well-known in network security world
‰ Bob, Alice (lovers!) want to communicate “securely”
‰ Trudy (intruder) may intercept, delete, add messages
Q: What can a “bad guy” do?
A: a lot!
eavesdrop: intercept messages
actively insert messages into connection
 impersonation: can fake (spoof) source address


Alice
Al
ce
data
channel
secure
sender
Bob
data, control
messages
i packet
in
k t ((or any fi
field
ld iin packet)
k t)
hijacking: “take over” ongoing connection by
removing sender or receiver, inserting himself
in place
 denial of service: prevent service from being
used by others (e.g., by overloading resources)

secure
receiver
data
more on this later ……
Trudy
Introduction
1-65
Introduction
1-66
11
Firewalls
Firewalls: Why
firewall
isolates organization’s internal net from larger
Internet, allowing some packets to pass,
blocking others.
prevent denial of service attacks:
 SYN flooding: attacker establishes many bogus
TCP connections, no resources left for “real”
connections.
prevent illegal modification/access of internal data.
 e.g., attacker replaces CIA’s homepage with
something else
allow only authorized access to inside network (set of
authenticated users/hosts)
two types of firewalls:
 application-level
 packet-filtering
public
Internet
administered
network
firewall
Introduction
‰ Virtual private network (VPN) is the fourth WAN
alternative.
‰ VPN communications are secure.
 The VPN client software encrypts, or codes, the original
messages so that its contents are hidden.
‰ A VPN uses the Internet or a private internet to
create the appearance of private point-to-point
connections.
‰ Virtual private networks offer the benefit of point
point-
‰ A VPN uses the public Internet to create the
to-point leased lines, and they enable remote
access, both by employees and by any others who
have been registered with the VPN server.
appearance of a private connection.
‰ A connection called a tunnel, is a virtual pathway
over a public or shared network from the VPN
client to the VPN server.
1-69
Introduction
1-70
Figure 5-19 Remote Access Using VPN:
Apparent Connection
Figure 5-18 Remote Access Using VPN:
Actual Connections
Introduction
1-68
Virtual Private Network
(Continued)
Virtual Private Network
Introduction
Introduction
1-67
1-71
Introduction
1-72
12
Figure 5-20 Wide Area Network Using
VPN
Criteria for Comparing Network
Alternatives
‰ Many different computer networking alternatives are
available, each with different characteristics.
‰ There are three types of costs that need to be
considered.



Introduction
Setup costs include the costs of acquiring transmission lines
and necessary equipment, such as switches, routers, and
access devices.
Operational costs include lease fees for lines and equipment,
charges of the ISP, the cost of ongoing training, etc.
Maintenance costs include those for periodic maintenance,
problem diagnosis and repair, and mandatory upgrades.
1-73
Criteria for Comparing Network
Alternatives (Continued)
Introduction
1-74
Introduction
1-76
Figure 5-21 Criteria for Comparing
Networking Alternatives
‰ There are six considerations with regard to
performance:






Speed
Latency
Availability
y
Loss rate
Transparency
Performance guarantees
‰ Other criteria to consider when comparing network
alternatives include the growth potential (greater
capacity) and the length of contract commitment.
Introduction
1-75
Domain Name System
Domain Name Registration
‰ IP addresses are useful for computer-to-computer
communication, but they are not well suited for human use.
‰ The purpose of the domain name system (DNS) is to
for administering the registration of domain names.
‰ ICANN does not register domain names itself;
convert user-friendly names into their IP addresses.
instead it licenses other organizations to register
names.
‰ Any registered, valid name is called a domain name.
‰ The process of changing a name into its IP address is
‰ ICANN is also responsible for managing the
called resolving the domain name.
name resolution system.
‰ Every domain name must be unique, worldwide.
‰ To ensure duplicate domain names do not occur, an agency
registers names and records the corresponding IP
addresses in a global directory.
Introduction
‰ ICANN is a nonprofit organization that is responsible
‰ The last letter in any domain name is referred to as
the top-level-domain (TLD).

1-77
domain
In the domain www.icann.org the top level domain is .org
Introduction
1-78
13
Domain Name Resolution
(Continued)
Domain Name Resolution (Continued)
‰ Domain name resolution is the process of converting a
domain name into a public IP address.
‰ A uniform resource locator (URL) is a document’s
address on the Web.
‰ The process starts from the TLD and works to the
left across the URL.
‰ URLs begin with a domain and then are followed by
p
data that locates a document with that
optional
domain.

‰ As of 2005, ICANN manages 13 special computers
called root servers that are distributed around the
world.
Thus, in the URL www.prenhall.com/kroenke , the domain
name is www.prenhall.com , and /kroenke is a directory
within that domain.
‰ Each root server maintains a list of IP addresses of
servers that each resolve each type of TLD.
Introduction
Introduction
1-79
1-80
Figure 5-25 Top-Level Domains,
2005
Domain Name Resolution (Continued)
‰ Domain name resolution proceeds quickly because
there are thousands of computers called domain name
resolvers that store the correspondence of domain
names and IP addresses


These resolvers reside at ISPs, academic institutions, large
companies, government organizations, etc.
For example,
example if a domain name solver is on your campus and
whenever anyone on your campus needs to resolve a domain
name, that resolver will store, or cache, the domain name and
IP address on a local file.
• When someone else on the campus needs to resolve the
same domain name, the resolver can supply the IP address
from the local file.
Introduction
Introduction
1-81
Internet History
Internet History
1961-1972: Early packet-switching principles
1972-1980: Internetworking, new and proprietary nets
‰ 1961: Kleinrock - queueing
theory shows
effectiveness of packetswitching
‰ 1964: Baran - p
packetswitching in military nets
‰ 1967: ARPAnet conceived
by Advanced Research
Projects Agency
‰ 1969: first ARPAnet node
operational
‰ 1970: ALOHAnet satellite
‰ 1972:




ARPAnet demonstrated
publicly
NCP (Network Control
Protocol) first host
hosthost protocol
first e-mail program
ARPAnet has 15 nodes
‰
‰
‰
‰
‰
Introduction
1-83
network in Hawaii
1973: Metcalfe’s PhD thesis
proposes Ethernet
1974: Cerf and Kahn architecture for
interconnecting networks
late70’s: proprietary
architectures: DECnet, SNA,
XNA
late 70’s: switching fixed
length packets (ATM
precursor)
1979: ARPAnet has 200 nodes
1-82
Cerf and Kahn’s
internetworking principles:
 minimalism, autonomy no internal changes
q
to
required
interconnect networks
 best effort service
model
 stateless routers
 decentralized control
define today’s Internet
architecture
Introduction
1-84
14
Internet History
Introduction: Summary
1990, 2000’s: commercialization, the Web, new apps
‰ Early 1990’s: ARPAnet
decommissioned
‰ 1991: NSF lifts restrictions on
commercial use of NSFnet
(decommissioned, 1995)
‰ early 1990s: Web
 hypertext [Bush 1945, Nelson
1960’s]
 HTML, HTTP: Berners-Lee
 1994: Mosaic, later Netscape
 late 1990’s:
commercialization of the Web
Covered a “ton” of material!
‰ Internet overview
‰ what’s a protocol?
‰ network edge, core, access
network
 packet-switching versus
circuit-switching
‰ Internet/ISP structure
‰ performance: loss, delay
‰ layering and service
models
‰ history
Late 1990’s – 2000’s:
‰ more killer apps: instant
messaging, P2P file sharing
‰ network security to
forefront
‰ est. 50 million host, 100
million+ users
‰ backbone links running at
Gbps
Introduction
Corporation during the 1990s, once said that humans are
incapable of thinking exponentially.

Instead, when something changes exponentially, we think of the
fastest linear change we can imagine and extrapolate from
there.
His point was that no one could then imagine how much growth
there would be in magnetic storage and what we would do with
it.
We have all witnessed exponential growth in a number of areas:
Internet connection, Web pages, and the amount of data
accessible on the Internet.
Introduction




What are the new opportunities?
What are the new threats?
How will our competition react?
How should we position ourselves?
How should we respond?
‰ Understand that technology does not drive people
to do things they’re never done before, no matter
how much the technologists suggest it might.
Introduction
1-88
though those six people do exist, we don’t know who
they are.
Today, in fact with the Internet, the number may be closer
to three people than five or six.

‰ Suppose
S
you wantt tto meett your university’s
i
it ’
Even worse, we often don’t know who the person is with whom
we want to connect.
‰ Most successful
f l professionals
f
l consistently
l build
ld
president.


‰ The problem with the six-degree theory, is that even
with the idea that everyone on earth is connected to
everyone else by five or six people.

thinking about ubiquitous and cheap connectivity
that is growing exponentially.
Reflection Guide–Human Networks
Matter More (Continued)
‰ The Hungarian writer, Frigyes Karinthy, came up

‰ Every business, every organization, needs to be
1-87
Reflection Guide–Human Networks
Matter More

1-86
Problem Solving Guide–Thinking
Exponentially Is Not Possible, but…
(Continued)
‰ Nathan Myhrvold, the chief scientist at Microsoft

follow!
Introduction
1-85
Problem-Solving Guide–Thinking
Exponentially Is Not Possible, but…

You now have:
‰ context, overview,
“feel” of networking
‰ more depth, detail to
The president has a secretary who acts as a gatekeeper.
If you walk up to that secretary and say, “I’d like a half
hour with President Jones,” you’re likely to be palmed off to
some other university administrator.
What else can you do?
Introduction
1-89
personal human networks.


They keep building them because they know that somewhere
there is someone whom they need to know or will need to
know.
They meet people at professional and social situations,
collect and pass out cards, and engage in pleasant
conversation (all part of a social protocol) to expand their
networks.
Introduction
1-90
15